1. Field of the Invention
This invention relates to rolls and more particularly, to elastomer rolls which are resistant to heat and have good releasing properties and are thus useful particularly as a fixing roll of electrostatic duplicators and the like apparatus.
2. Description of the Prior Art
In an electrostatic duplicating system where a toner image formed on a paper sheet is fixed, the toner image-bearing paper sheet is passed between two rolls contacted under pressure. One or both of the rolls are ordinarily heat rolls which are arranged to be heated from the inside. The fixing system using the heat roll or rolls is higher in heat efficiency than other systems using, for example, an oven. Thus, the heat roll fixing system is more advantageous in that high speed duplicating operations are readily realized. From this point of view, recent electrostatic duplicators have adopted this manner of fixing.
The rolls used in the fixing method are ordinarily comprised of a core bar of a metal such as aluminum, stainless steel, iron and the like, an elastic rubber layer formed on the core metal and made, for example, of fluorine rubber, silicone rubber or the like, and a fluorine resin layer formed as an upper most layer. The fluorine resin used for this purpose may be tertrafluorethylene-perfluoroalkoxyethylene copolymers (which may be hereinafter abbreviated as PFA), polytetrafluoroethylene resin (which may be hereinafter abbreviated as PTFE), a fluorinated ethylene propylene resin or tetrafluoroethylene-hexafluoropropylene resin (which may be hereinafter abbreviated as FEP) or the like. For the formation of the fluorine resin layer, it is necessary to heat the roll having the rubber layer at a temperature of from 300 to 400.degree. C. for 30 minutes to 2 hours so that the fluorine resin is melted and adhered to the rubber layer. This will cause the underlayer of the rubber to thermally deteriorate and may result in an extreme lowering of the hardness of the rubber layer. If the fluorine resin is melt-adhered at a low temperature of not higher than 300.degree. C. in order to avoid the above problem, the releasing properties of the fluorine resin layer becomes unsatisfactory. In addition, the adhesion between the rubber layer and the uppermost fluorine resin layer becomes so weak that the fluorine resin layer tends to peel off or blister at part or all of the surface of the roll in long use. Thus, the durability is not satisfactory.